​Watts (Wattage): The amount of electricity an ojbect needs to work (or how much energy it emits when running).

Here's an analogy...

All the water in the system, kept in the tank, creates pressure.

Water flowing to the job site is measured and regulated.

The item being powered is then able to complete a task, exerting and expelling energy.

Lucky for filmmakers, we don't have to master the science behind electrons, protons, and neutrons in order to use lights. We can simply do a simple equation to figure out how many lights we can plug in to each circuit!

What's a Circuit?

Notice in this image above that wires run to every room in the house. Some rooms are grouped together on the same (colored) circuit and share the same power supply. This means that if someone trips the circuit (drawing too much power) in one room then all the rooms will lose power.

A circuit is where electricity enters and loops through an electrical system.

In a circuit, electricity enters and loops through an electrical system. In the image on the left, electricity is entering and existing the light bulb. The image on the right explains that the electricity exiting out of the light bulb is equal to the amount of electricity going in.

Where to Start?

In the United States, a typical house has:

A circuit breaker box (to regulate all power)

100 - 150 Amps circulating in total (split up between circuits)

110 - 120 Volts of pressure in each circuit

Outlets grouped in ciruits have 120V / 240V pressure and 20 Amps of available electricity

For example:

Kitchens usually have two circuits because the oven, refridgerator, microwave, and dishwasher all draw a lot of power. Each circuit is likely 20 Amps or more.

The dining and living rooms are usually paired together on a single cicuit because of typically low electrical needs.

Bathrooms are usually on their own circuit because hairdryers draw a lot of power.

Bedrooms are usually grouped together, which can be problematic during New England summers with window unit airconditioners.

Laundryroom is likely on it's own circuit as well because of the washer and dryer.

These images above show the same setup for a breaker box; a main line entering at the top, 120v and 240v breakers for a variety of circuits, a ground line, and a neutral line.

IMPORTANT NOTE: The circuit breaker box is important to filmmakers because it tells us which rooms are grouped together and which rooms share the same 20 amps of power.

So...where do we plug in our lights?

Here's where the math comes in...

Watts = Volts x Amps

Mock Scenario

You have three Lowel Tota lights that you need to light up a living room scene. Each light draws / uses 800 watts.

Look over the house floor plan to study the living room.

Look at the circuit breaker box picture to see what rooms are on each circuit.;

"LVD" means liviging room/dining room for this house.

Assignment:

​Figure out how many of these lights we can plug into the LVD circuit.

Figure out if we need to plug in any lights anywhere else in the house.​

Process

3 Lowel Tota Lights (800W + 800W + 800W) = 2400 Watts

Formula: Wattage = Volts x Amps

2400W = 110V (Standard USA Outlet) x Amp

​Solve for Amps!

Divide both sides by 120V; meaning 2400/120 = 20 Amps

Result: The three lights combined will push the circuit to capacity.

Answer Summary

We should plug two lights into the Living Room / Dining Room (LVD) and then the third light into an outlet in the kitchen.

If a typical American house has only 20 Amps per circuit then we can plug in TWO of these lights into ONE circuit (drawing about 14 Amps).

However, we need to plug the LAST light into a DIFFERENT circuit (which will draw about 7 Amps).